All O3 observational data and aggregates on this EMEP TFMM wiki was processed by NILU/EMEP-CCC

Data were extracted for three periods
1990-2001
1990-2012
2002-2012

For each period the monitoring sites were selected based on:
 >75 % data capture each year in > 75 % of the years

The raw hourly data are given in the proxy "ug/m3" as used in EBAS. 
The conversion factor to ppb is 2 at nearly all sites (1 ppb = 2 ug/m3)
Consult the EMEP ozone data report (www.emep.int) for details about this. 

All AOT40 data are given in ppb hours. They are computed according to the
UNECE convention, i.e. for hours when the global radiation > 50 W/m2 
based on zenith angle and climatological data for the relationship 
between radiation and zenith angle. 


All trends were calculated by a Mann Kendall method (Gilbert, 1987) programmed
in IDL by NILU. Please note that all ozone trend data are given in ppb whereas
the raw hourly data are in proxy "ug/m3" as mentioned above. 

The slopes refer to Sen's slope. 
Relative slopes refer to the start year 
  i.e. if y = a + b(t-t0) then rel.slope = b/y(t=t0)


Details about the trend metrics:
  annual means are calculated based on the mean of the daily means
  SOMO35 is the sum over the year of the daily max 8h running means above 35 ppb
  SOMO10 is the sum over the year of the daily max 8h running means above 10 ppb

  The daily max 8h running mean is allocated to the day for which the last hour 
  of the 8h period ends
